Heparin is sulfate-containing polysaccharide which on a large scale is isolated from intestinal mucus from swine or lung from cattle. The average molecular weight for standard bovine heparin is more than 9,000 daltons and for standard porcine heparin more than 12,000 daltons. Traditionally, the clinical use of heparin has been associated with its anticoagulant and antithrombotic properties (Jorpes, Heparin in Treatment of Thrombosis, 2nd Ed. Oxford Medical Publications (1946)). Although the exact mechanism for heparin's antithrombotic properties is not known, it is believed to act by binding to antithrombin III. The heparin-antithrombin III complex inhibits the activity of numerous enzymes in the clotting cascade, including factors II (thrombin), IX/IXa, X/Xa, XI/XIa, and XIII (Carter et al., Ann. Pharmacotherapy, 27:1223-30 (1993); Buckley et al., Drugs, 44:465-97 (1992)). In addition, heparin induces release of other endogenous antithrombotic substances, such as tissue factor pathway inhibitor and tissue plasminogen activator. Heparin has also been found to accelerate coronary collateral development in dogs (Fujita et al., Japanese Circulation Journal, 51: 395-402 (1987)) and to improve collateral circulation in patients with effort angina (Fujita et al., Circulation, 77:1022-1029 (1988)). Other effects such as the “anti-complementary power of heparin” recognized by Ecker et al. in J. Infect. Dis. 44:250-253 (1929) and the finding by Clowes et al. in Nature 265:625-626 (1977) that heparin infusion following experimental injury suppressed the proliferation of smooth muscle cells, have not led to any widespread use of heparin for the treatment of diseases related to inflammation or to arteriosclerosis, which are associated with complement activation and smooth muscle cell proliferation respectively. The risk of hemorrhage is considered to be the main limitation for the clinical use of heparin in non-antithrombotic indications.
Angiogenesis is the development of new blood vessels from preexisting blood vessels (Mousa, In: Angiogenesis Inhibitors and Stimulators: Potential Therapeutic Implications, Landes Bioscience, Georgetown, Tex.; Chapter 1 (2000)). Physiologically, angiogenesis ensures proper development of mature organisms, prepares the womb for egg implantation, and plays a key role in wound healing. On the other hand, angiogenesis supports the pathological conditions associated with a number of disease states such as cancer, inflammation, and ocular diseases.
The development of vascular networks during embryogenesis or normal and pathological angiogenesis depends on growth factors and cellular interactions with the extracellular matrix (Breier et al., Trends in Cell Biology 6:454-456 (1996); Folkman, Nature Medicine 1:27-31 (1995); Risau, Nature 386:671-674 (1997)). Blood vessels arise during embryogenesis by two processes: vasculogenesis and angiogenesis (Blood et al., Bioch. Biophys. Acta 1032:89-118 (1990)). Vascular endothelial growth factor (“VEGF”), basic fibroblast growth factor (“bFGF” or “FGF2”), interleukin 8 (“IL-8”) and tumor necrosis factor alpha (“TNF-α”) are some of the growth factors that play a role in pathological angiogenesis associated with solid tumors, diabetic retinopathy, and rheumatoid arthritis (Folkman et al., Science 235:442-447 (1987)). Angiogenesis is generally absent in adult or mature tissues, although it does occur in wound healing and in embryogenesis (Moses et al., Science 248:1408-1410 (1990)).
Angiogenesis or “neovascularization” is a multi-step process controlled by the balance of pro- and anti-angiogenic factors. The latter stages of this process involve proliferation and the organization of endothelial cells (EC) into tube-like structures. Growth factors such as FGF2 and VEGF are thought to be key players in promoting endothelial cell growth and differentiation. The endothelial cell is the pivotal component of the angiogenic process and responds to many cytokines through its cell surface receptors and intracellular signaling mechanisms. Endothelial cells in culture are capable of forming tube-like structures that possess lumens. Therefore, endothelial cells are not only a prerequisite for neovascularization, but appear to be the basal structural requirement as well.
It has been proposed that inhibition of angiogenesis would be a useful therapy for restricting tumor growth Inhibition of angiogenesis can be achieved by inhibiting endothelial cell response to angiogenic stimuli as suggested by Folkman et al., Cancer Biology 3:89-96 (1992), where examples of endothelial cell response inhibitors such as angiostatic steroids, fungal derived products such fumagilin, platelet factor 4, thrombospondin, alpha-interferon, vitamin D analogs, and D-penicillamine are described. For additional proposed inhibitors of angiogenesis, see Blood et al., Bioch. Biophys. Acta 1032:89-118 (1990), Moses et al., Science 248:1408-1410 (1990), and U.S. Pat. Nos. 5,092,885, 5,112,946, 5,192,744, and 5,202,352.
Native heparin or heparin fractions have also been proposed for use in the inhibition of angiogenesis. However, such use has not been widely accepted due to the high anticoagulant activity of such native heparin and heparin fractions. In particular, as described above, the risk of bleeding complications is considered to be the main limitation for the clinical use of heparin in non-antithrombotic indications.
The present invention is directed to overcoming these and other deficiencies in the art.